1. Technical Field
The present invention relates to the field of array antennas and more particularly to array antennas having extremely wide bandwidth.
2. Description of the Related Art
Phased array antenna systems are well known in the antenna art. Such antennas are generally comprised of a plurality of radiating elements that are individually controllable with regard to relative phase and amplitude. The antenna pattern of the array is selectively determined by the geometry of the individual elements and the selected phase/amplitude relationships among the elements. Typical radiating elements for such antenna systems may be comprised of dipoles, slots or any other suitable arrangement.
In recent years, a variety of new planar type antenna elements have been developed which are suitable for use in array applications. One example of such an element is disclosed in U.S. application Ser. No. 09/703,247 to Munk, et al. entitled Wideband Phased Array Antenna and Associated Methods (hereinafter xe2x80x9cMunkxe2x80x9d). Munk discloses a planar type antenna-radiating element that has exceptional wideband characteristics. In order to obtain exceptionally wide bandwidth, Munk makes use of capacitive coupling between opposed ends of adjacent dipole antenna elements. Bandwidths on the order of 9-to-1 are achievable with the antenna element with the Munk et al. design. Analysis has shown the possibility of 10-to-1 bandwidths achievable with additional tuning. However, this appears to be the limit obtainable with this particular design.
Although the Munk et al. antenna element has a very wide bandwidth for a phased array antenna, there is a continued need and desire for phased array antennas that have even wider bandwidths exceeding 10-to-1. Past efforts to increase the bandwidth of a relatively narrow-band phased array antenna have used various techniques, including dividing the frequency range into multiple bands.
For example, U.S. Pat. No. 5,485,167 to Wong et al. concerns a multi-frequency phased array antenna using multiple layered dipole arrays. In Wong et al., several layers of dipole pair arrays are provided, each tuned to a different frequency band. The layers are stacked relative to each other along the transmission/reception direction, with the highest frequency array in front of the next lowest frequency array and so forth. In Wong et al., a high band ground screen, comprised of parallel wires disposed in a grid, is disposed between the high-band dipole array and a low band dipole array.
Wong""s multiple layer approach has two drawbacks. The dual layer approach makes manufacturing and connecting the elements more difficult due to the embedded interconnects of a multiple layer antenna. Second, in a multiple layer antenna the upper elements will present some amount of blockage to the lower (closer to the ground plane) elements. Moreover, conventional dipole arrays as described in Wong et al. have a relatively narrow bandwidth such that the net result of such configurations may still not provide a sufficiently wideband array. Accordingly, there is a continuing need for improvements in wideband array antennas that have a bandwidth exceeding 10-to-1.
The invention concerns an array of radiating elements. A first plurality of antenna elements in a first plane in an array configuration is configured for operating on a first band of frequencies. A second plurality of planar antenna elements in an array configuration is configured for operating on a second frequency band, the second plurality of antenna elements is also positioned in the first plane. A first effective ground plane is provided for the first plurality of antenna elements and a second effective ground plane is provided for the second plurality of antenna elements. A first spacing between the first plurality of elements and the first effective ground plane is different from a second spacing between the second plurality of elements and the second effective ground plane. According to one embodiment, the second plurality of elements are adjacent to one another in a unitary cluster that is disposed within the first plurality of elements.
The array can also comprise a plurality of RF feed points connected to the first and second plurality of antenna elements and a controller for controlling phase and/or amplitude of RF applied to the radiating elements at the feed points. This configuration allows the array to be scanned as needed to advantageously direct the received or transmitted RF energy.
According to one aspect of the invention, the first plurality of elements can be low band antenna elements for operating on a lower band of frequencies, whereas the second plurality of elements are high band antenna elements for operating on a relatively higher band of frequencies. In that case, the first spacing is greater than the second spacing.
According to yet another aspect of the invention, the second plurality of antenna elements can define a high frequency cluster or antenna elements. A plurality of such high frequency clusters can be disposed among the first plurality of antenna elements. Each of the high frequency clusters can be configured to operate on the same band of frequencies or can be configured for a band of frequencies distinct from other high frequency clusters.
A ground plane stepped portion can be provided where the first effective ground plane transitions from the first spacing to the second spacing defining the second effective ground plane. Alternatively, the second effective ground plane can be a low pass frequency selective surface interposed between the second plurality of antenna elements and the first effective ground plane. In any case, at least one dielectric layer is preferably interposed between the first plane, where the first and second plurality of antenna elements are located, and the respective effective ground planes for each set of elements.
According to one embodiment, one or both of the first and second plurality of antenna elements can comprise an elongated body portion, and an enlarged width end portion connected to an end of the elongated body portion. The enlarged width end portions of adjacent ones of the antenna elements comprise interdigitated portions. More particularly, the plurality of antenna elements can be comprised of adjacent dipole elements, and an end portion of each dipole element can be capacitively coupled to a corresponding end portion of an adjacent dipole element.